1. Field of the Invention
The present invention relates to an ironing punch for making the socket of a ball-and-socket joint for use as a constant-velocity universal joint or the like, and a method of manufacturing such an ironing punch.
2. Description of the Prior Art
The socket of a ball-and-socket joint comprises a cup-shaped socket body and an attachment shaft projecting outwardly from an outer surface of the bottom wall of the cup-shaped socket body. The cup-shaped socket body has a spherical inner surface with its center of curvature being positioned within the cup-shaped socket body. The spherical inner surface has a plurality of ball-rolling grooves extending along the generator thereof. A retainer-sliding surface is defined between each pair of adjacent ball-rolling surfaces. Each of the ball-rolling grooves has an arcuate portion extending in an intermediate region between an open end of the cup-shaped socket body and an inner surface of the bottom wall thereof and held substantially concentric with the retainer-sliding surfaces, a first straight portion extending from the arcuate portion to the open end, and a second straight portion extending from the arcuate portion to the inner surface of the bottom wall.
When the socket of the above structure is to be manufactured, a cup-shaped member of a socket blank is placed over an ironing punch, and ironed by a die which is forcibly squeezed over the peripheral wall of the cup-shaped member. The punch comprises a punch body and a plurality of ridge-shaped dies mounted on the punch body. The punch body has a distal end surface to be positioned in confronting relation to the inner surface of the bottom wall of the cup-shaped member. The punch body also has a plurality of ridges on the outer peripheral surface thereof for forming the ball-rolling grooves in the spherical inner surface of the cup-shaped socket body, the ridges extending from the distal end surface in the direction in which the cup-shaped member is ironed. The ridge-shaped dies are slidably fitted in grooves between the ridges, and serve to form the respective retainer-sliding surfaces on the spherical inner surface of the cup-shaped socket body.
Each of the ridges has a first forming region for forming one of the first straight portions of the ball-rolling grooves, a surface forming region for forming one of the retainer-sliding surfaces, and a second forming region for forming one of the second straight portions of the ball-rolling grooves. The distance between the crest surface of the first forming region and the crest surface of the surface forming region adjacent thereto is selected to be greater than the distance between the crest surface of a forming region for forming each of the arcuate portions and the second forming region and the crest surface of the surface forming region adjacent thereto.
The ridges of the punch body are grounded with the ridge-shaped dies being assembled on the punch body. Since the distance between the crest surface of the first forming region and the crest surface of the surface forming region adjacent thereto is greater than the distance between the crest surface of the forming region for forming the arcuate portion and the second forming region and the crest surface of the surface forming region adjacent thereto, as described above, a grinding wheel for grinding the ridges has an outer circumferential grinding surface matching the finished shape of the forming region for forming the arcuate portion, thereby avoiding physical interference between the grinding wheel and the ridge-shaped dies.
The grinding wheel can grind the forming regions for forming the arcuate portions and also the first forming regions for forming the first straight portions. However, the grinding wheel cannot grind the bottom or skirt areas of the first forming regions for forming the first straight portions.
It has been customary to finish the bottom or skirt areas of the first forming regions with an electric discharge process and then a manual grinding process. The conventional finishing practice is however inefficient and results in an increase in the cost of the punch.